As far as settings go, there are no hard and fast rule; it's really whatever it takes to get you the result you want. Generally, I prefer to shoot with a fairly large aperature (small f#) to help soften the background focus and reduce distractions.
With respect to your latest two images. The top one is very nice. Exposure-wise, it's just a little too bright; you can see that you've lost some detail in her white shirt, BUT that's minor. I would level this image and crop much more tightly and clone out the orange float in the background. I think that will give you a really strong image. In the second, the hair lighting is wonderful, unfortunately, the face is under-exposed by probably two full stops. Fill-flash would have save this and given you a really nice shot. If you shot this in RAW, you can probably massage the exposure by quite a bit. If it's .jpg only, you can still improve it somewhat. I would take it back to the pixel room and see what you can do with the levels/curves adjustments and exposure controls.